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Full text of "Flora Indica Vol-I"

INTRODUCTORY  ESSAY                                   99
Of the tropical and subtropical plants that accompany this
high summer temperature and withstand the cold of consider-
able elevations, are many of those mentioned towards the
commencement of this section as natives of dry tropical forests
with contrasted seasons, at the level of the sea or on plains
raised but little above it. Populus Euphratica, a Gynanchum,
Chloris barbata, and Cyperus aristatus, all of which ascend
to 11,000 feet in Ladak, are other remarkable instances, as is
Pegamum Harmala, which attains 9000 feet.
In the Himalaya the truly temperate vegetation supersedes
the subtropical above 4000-6000 feet; and the elevation at
which this change takes place corresponds roughly with that
at which the winter i^s marked by an annual fall of snow.
This phenomenon varies extremely with the latitude, longi-
tude, humidity, and many local circumstances. In Ceylon
and the Madras Peninsula, whose mountains attain 9000 feet,
and where considerable tracts are elevated above 6-8000 fefet,
snow has never been known to fall. On the Khasia moun-
tains, which attain 7000 feet, and where a great extent of
surface is above 5000, snow seems to be unknown. In Sik-
kim snow annually falls at about 6000 feet elevation, in Nipal
at 5000 feet, in Kumaon and Garhwal at 4000, and in the
extreme West Himalaya lower still.
It is hence only on the Himalaya and Mishmi mountains
that a purely temperate flora prevails, to the exclusion of all
tropical forms \ though in Ceylon, the Nilghiri mountains, and
Khasia, -the temperate forms are very numerous, and so pre-
valent on the highest summits as tp render it very desirable
that these heights should be subjected to a very close botani-
cal examination. Local circumstances, again, seem to bring
the temperate forms lower upon the Khasia and Nilghiri moun-
tains than upon, the Himalaya, which are further north ; and
of these causes the fact that the exposed flat or undulated
surfaces of the Khasia are swept by violent winds, is one of
the most powerful. The contrast in this respect between the
Khasia and the Sikkim-Himalaya is very remarkable, many